I always use front and rear blinkies during the day.
I'm 99.99% sure the front blinky has made a difference. Prior to the front blinky, cars would periodically not see me and I'd be doing a "brake check" to not hit them as they entered my lane. Then, I was nearly hit head-on when a car decided to pass another on a two-lane road (one lane each way) and ran me off the road. Since adding the front blinky - years ago - I can think of only one incident where I was 'not seen'.
So I have little doubt about the effectiveness of the front blinky. The rear blinky? I can't say I got rear-ended before but not after (which is a GOOD thing), but I'd like to think it has a positive effect.
Note: don't cheap-out on lights or batteries. I sometimes encounter a rider who I think forgot to turn their rear blinky on. As I get closer, I realize it's either a 99 cent China cheapo, or the batteries are almost dead (or both). For the daytime rider, bright enough lights can be had for $20-$25 each, front and rear.
Last edited by JohnnyCyclist; 04-25-16 at 02:21 PM.